1. Field of the Invention
This invention relates to improved electrophotoconductive materials and photosensitive members utilizing the electrophotoconductive materials. More particularly, it relates to an improved cadmium sulfo-selenide host activated with copper and chlorine having controlled levels of selenium and chloride, a small particle size and a narrow particle size distribution and the surfaces free of p-type copper sulfide which enables improved contrast when such material is employed as an electrophotoconductor in equipment utilized in an electrophotographic reproduction process.
2. Prior Art
Photoconductive materials are known and have a variety of uses in photoelectric devices, photoelectric relay devices and the like. Electrophotoconductive materials useful in electrophotographic process and apparatus, while of the same generic type of material have to have different properties. A small particle size material is usually required in electrophotographic application; normally from 1 to 2 micrometers. The small particle size material has a high response to visible light excitation, while other electrophotographic materials have their highest response in the ultraviolet, for example Se and ZnO. While neither Se nor ZnO to be activated with other elements, CdS and Cd(S,Se) are usually activated with copper or silver in order to enhance their photo response.
Prior art electrophotoconductive materials are disclosed in a number of sources. For example, U.S. Pat. No. 3,666,363 discloses a mixture of CdS and a ternary compound of the formula X.sub.4 YZ.sub.6 wherein X is Zn or Cd, Y is Si or Ge and Z is S, Se and Te. Such a mixture is used for color reproduction.
U.S. Pat. No. 3,743,609 discloses a process for firing mixtures of cadmium sulfide, cadmium selenide or cadmium sulfoselenide in the presence of a suitable activator, a flux and a dispersant. The foregoing process provides a material which has a fine particle size, however, the material tends to degrade when used in electrophotographic processes and does not exhibit a high differential between the image voltage and the background voltage. While such materials are suitable for copying black and white materials the contrast is not sufficient to enable a clear copy over a long period of time. Additionally, one of the major difficulties with the present day copiers is the reproduction in black and white of documents that contain color. Although color reproductions can be made by other processes, e.g., photographic process, often in many instances it is desirable to make a black and white copy of information contained in color display on the original (for example, graphs and certain printings displayed in color on the original for certain effects). Another problem that sometimes exists is that original copies do not always have a good contrast. With present materials, an unclear copy can result because the differential between the image and background voltage, hereinafter referred to as contrast voltage, is not great enough to enable sufficient contrast between the printing on the paper and the paper color. Additionally, the prior art materials tended to degrade and the photosensitive members which contain a base of a conductive material, an electrophotoconductive layer overlying the conductive base and an insulating layer overlying the electro-photoconductive layer, had to be replaced after the electrophotographic process was used to run several copies.
It is believed, therefore, that an electrophotoconductive material which has a desired particle size and narrow particle size distribution, exhibits a large contrast voltage and which does not degrade even after upon prolonged usage would be an advancement in the art.